MAJOR SPOILER or not but its about the first life.
Idk if this really is true but probably is. I found this spoiler somewhere.
So in the original story/the book claude actually has a sad death. The flashbacks you saw are actually how he died. After he executed the original athy, he started to spend more time with jennette, which gave him more headaches and he started to lose memories. Felix wasn't there anymore, he left claude after claude executed athy. He didn't have anyone to trust anymore so he endured the pain and died. The black haired guy/ claude's older brother is the one who planned it all. The older brother asks jennette if she wants to die with claude or live as the princess. She chose to live as the princess, but had a bad trauma. She blamed herself for athys death, so she starts practicing black magic. She makes a deal with a black magician to turn back the time, so she can save her sister. But when the magician turned back the time everyone forgot the memories of the first life. This is where the magician picks a soul from another dimension and gets her/the soul to read the book about thr lovely princess, so she is the only one that remembers the first time. Thr magician then kills the soul in her sleep so she reincarnates as Athy. Lucad then remembers the first life after he eats the world fruit. DON'T WORRY This BOOK HAS A GOOD ENDING :)
THE DAD IS SO FINE!!!!!!!!!